Mercury-containing and mercury-free lamps, in particular discharge lamps for use in motor vehicles (so-called D lamps), each have very different properties. This applies in particular to the electrical properties of the two lamp types, which demonstrate the same rated power of 35 watts during steady-state operation, but the mercury-free lamp only has approximately half the running voltage in comparison with the mercury-containing lamp. Even during startup, the two lamp types need to be operated very differently than one another in order to achieve the desired requirements, such as sufficiently high instantaneous luminous flux alongside an acceptable life.
Therefore, a dedicated electronic ballast type is used in the prior art for each lamp type (Hg-containing D1 lamp and Hg-free D3 lamp), the respective electronic ballast type individually taking into consideration the particular features of the associated lamp type. Although the two electronic ballast types are based on a common hardware and software concept, the detailed requirements of the lamps do not make it possible to exchange the electronic ballasts for one another.
This results in the disadvantage that, during production, it is necessary to distinguish between two hardware and two software variants and then two products need to be managed both in terms of sales and by the customer, which firstly means twice the storage requirement and secondly often results in confusion.
In order to reduce the possibility of confusion, it has been proposed in the prior art to use different plug codings. However, this has the result that different cables are also required in addition to the different electronic ballasts and lamps.
The patent application EP 0 759 686 A2 has proposed a method and a circuit arrangement in which the electronic ballast has a microprocessor which identifies the individual lamp type connected to the electronic ballast and drives the lamp depending on the lamp type specification identified.
For this purpose, the lamp-type-specific codings arranged on the lamp, such as knobs arranged on the lamp base, for example, which owing to their number and arrangement form a lamp-type-specific coding, are detected and the lamp is driven correspondingly to previously stored operational parameters for this lamp type. Another possibility of lamp type identification consists in detecting a bar code applied to the lamp. Furthermore, there is the possibility of additionally using electrical variables for lamp type identification.
One disadvantage with this prior art, however, is the fact that each time the lamp is switched on there is a delay while the electronic ballast determines the lamp type in question. Therefore, this procedure is unsuitable precisely for application in motor vehicles since in this case it is necessary for the lamp to be started up particularly quickly. This is also the reason why the lamp power is increased to a multiple of the rated power during startup (so-called power startup).